Polyamides are synthetic polymers which are widely used in many industrial applications. Particularly, a well-known use of polyamides resides in the field of manufacturing automotive parts, which have high requirements for stiffness, mechanical strength, dimensional stability, and physical/chemical resistance to the environment they are exposed to. In order to meet these requirements, it is usually desired that the polyamides be modified: either by the addition of different additives or by blending them with another polymeric material.
For instance, U.S. Pat. No. 5,486,594 (SHELL OIL COMPANY) Jun. 11, 1994 describes a modified polyamide composition comprising 80 to 85 weight percent of a polyamide selected from Nylon 6, Nylon 11 and Nylon 12 and from 15 to 20 weight percent of a polyketone as a Nylon toughener. Noticeably, as observed in the Examples of U.S. Pat. No. 5,486,594, the amount of polyketone additive in the modified polyamide composition is required to reach at least 15 weight percent, otherwise the desired impact toughening effect would not be happening.
Nevertheless, blending a significant amount of polyketone into a polyamide composition is known to be difficult, as there is the risk of crosslinking or decomposition. Moreover, due to the curing properties of polyketones (by heating or by light irradiation), excessive use of this polymer in automotive parts would raise their recycling difficulty.
Aiming to solve this blending problem, U.S. Pat. No. 6,150,474 (EMS-INVENTA AG) Dec. 22, 1998 provides a polyamide-polyketone blend composition in which the polyamide is prepared to have a clear surplus of COOH groups. More specifically, as revealed from the Examples of U.S. Pat. No. 6,150,474, a stable polyamide-polyketone blend was only achieved for polyamides in which the NH2 end-group concentration is less than 15 μeq/g and the carboxyl end-group concentration is at least 80 μeq/g. In comparison, blend samples not meeting these end-group concentration criteria showed no extrudability due to decomposition reactions.
Apart from the abovementioned compounding/extruding difficulties, a polyamide based composition blended with a minor amount of polyketone is also found to be susceptible to salt stress induced corrosion cracking, a property that makes it a less-desirable material for vehicle components. This is because, in colder climate, the vehicle components are sometimes exposed to salts such as sodium chloride or calcium chloride which are used to melt snow and ice.
Furthermore, a polyamide based composition blended with a minor amount of polyketone also fails to provide reliable glycol resistance, which is a crucial property for vehicle parts which are exposed to anti-freezing agents.
Therefore, the need was felt to have new, improved polyamide-polyketone blends, which circumvent the prior art limitations by providing good extrudability and excellent chemical resistance in a composition that is easy to compound and recycle.
The Applicant has now found that by combining a rubber component and a minor amount of polyketone in a polyamide based composition, the above technical object can be achieved.